Evolution of the jaw

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What do you know…just last week, I posted an article dismissing a creationist’s misconceptions about pharyngeal organization and development, in which he asks about the evidence for similarities between agnathan and gnathostome jaws, and what comes along but a new paper on the molecular evidence for the origin of the jaw, which describes gene expression in the lamprey pharynx. How timely! And as a plus, it contains several very clear summary diagrams to show how all the bits and pieces and molecules relate to one another.

The short summary is that there is a suite of genes (the Hox and Dlx genes, which define a cartesian coordinate system for the branchial arch elements, Fgf8/Dlx1 genes that establish proximal jaw elements, and Bmp4/Msx1 genes that demarcate more distal elements) that are found in both lampreys and vertebrates in similar patterns and roles, and that vertebrate upper and lower jaws are homologous to the upper and lower “lips” of the lamprey oral supporting apparatus.

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Coelacanth evolution

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I was reminded of one of the more comical, but persistent misconceptions by creationists in a thread on Internet Infidels, on The Coelacanth. Try doing a google search for “coelacanth creation” and be amazed at the volume of ignorance pumped out on this subject. I’ve also run across a more recent example of the misrepresentation of the coelacanth that I’ll mention later … this poor fish has a long history of abuse by creationists, though, so here’s a brief rundown of wacky creationist interpretations.

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Another biologist tries to make the science accessible

Here’s a nicely focused blog: R. Ford Denison, of the UM Department of Ecology, Evolution, and Behavior, has a new blog titled This Week in Evolution, and he’s planning to put up one post each week summarizing a recently published paper in evolutionary biology. He has specific criteria:

Each week, I plan to discuss a scientific paper that meets the following criteria:

  1. published during the previous month;
  2. about some aspect of evolution;
  3. published after peer review in a journal with a citation impact of at least 1.0 (i.e., no third-tier journals);
  4. containing significant amounts of data, not just mathematical modeling or discussion.

It’s an excellent plan—check in each week!

Orthozanclus

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(click for larger image)
Reconstruction of O. reburrus by M. Collins. The precise arrangement of the anteriormost region remains somewhat conjectural.

Halkieriids are Cambrian animals that looked like slugs in scale mail; often when they died their scales, called sclerites, dissociated and scattered, and their sclerites represent a significant component of the small shelly fauna of the early Cambrian. They typically had their front and back ends capped with shells that resembled those we see in bivalve brachiopods. Wiwaxiids were also sluglike, but sported very prominent, long sclerites, and lacked the anterior and posterior shells; their exact position in the evolutionary tree has bounced about quite a bit, but some argument has made that they belong in the annelid ancestry, and that their sclerites are homologous to the bristly setae of worms. One simplistic picture of their relationship to modern forms was that the halkieriids expanded their shells and shed their scales to become molluscs, while the wiwaxiids minimized their armor to emphasize flexibility and became more wormlike. (Note that that is a very crude summary; relationships of these Cambrian groups to modern clades are extremely contentious. There’s a more accurate description of the relationships below.)

Now a new fossil has been found, Orthozanclus reburrus that unites the two into a larger clade, the halwaxiids. Like the halkieriids, it has an anterior shell (but not a posterior one), and like the wiwaxiids, it has long spiky sclerites. In some ways, this simplifies the relationships; it unites some problematic organisms into a single branch on the tree. The question now becomes where that branch is located—whether the halwaxiids belong in a separate phylum that split off from the lophophorate family tree after the molluscs, or whether the halwaxiids are a sister group to the molluscs.

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Hey, this Joachim Bublath guy is good!

A reader pointed me to this German documentary (with English subtitles) on evolution and creationism—it has a nice 10 minute primer on mechanisms and evidence for evolution (with evo-devo, especially of fruit flies and zebrafish, prominently mentioned, appropriately enough for the country of Christiane Nusslein-Volhard).

There’s also a segment on creationism that is a bit lacking in nuance—they are all lumped together as young earth creationists—which is the kind of opening creationists use to disavow association with those other kooks, while glossing over the foolishness they do believe. Never mind the theological hairsplitting, though, YECs and IDist are fundamentally identical in their rejection of science for dogma.

Aside from that, it’s a simple introduction to evolution that emphasizes the molecular evidence (yay!), has eye-catching graphics and animations, and scathingly dismisses creationism and the general descent into mystical thinking. Do any of my German readers know of this fellow? Was this broadcast on German television?

Basics: Gastrulation, invertebrate style

The article about gastrulation from the other day was dreadfully vertebrate-centric, so let me correct that with a little addendum that mentions a few invertebrate patterns of gastrulation—and you’ll see that the story hasn’t changed.

Remember, this is the definition of gastrulation that I explained with some vertebrate examples:

The process in animal embryos in which endoderm and mesoderm move from the outer surface of the embryo to the inside, where they give rise to internal organs.

I described frogs and birds and mammals the other day, so lets take a look at sea urchins and fruit flies.

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The Haeckel-Wells Chronicles

Lately, the Discovery Institute has stuck its neck out in response to the popularity of showings of Randy Olson’s movie, Flock of Dodos, which I reviewed a while back. They slapped together some lame critiques packaged on the web as Hoax of Dodos (a clunker of a name; it’s especially ironic since the film tries to portray the Institute as good at PR), which mainly seem to be driven by the sloppy delusions of that poor excuse for a developmental biologist, Jonathan Wells. In the past week, I’ve also put up my responses to the Wells deceptions—as a developmental biologist myself, I get a little cranky when a creationist clown abuses my discipline.

In case you are completely baffled by this whole episode, here’s a shorter summary.

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Wells and Haeckel’s Embryos

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(This is a rather long response to a chapter in Jonathan Wells’ dreadful and most unscholarly book, Icons of Evolution)

The story of Haeckel’s embryos is different in an important way from that of the other chapters in Jonathan Wells’ book. As the other authors show, Wells has distorted ideas that are fundamentally true in order to make his point: all his rhetoric to the contrary, Archaeopteryx is a transitional fossil, peppered moths and Darwin’s finches do tell us significant things about evolution, four-winged flies do tell us significant things about developmental pathways, and so forth. In those parts of the book, Wells has to try and cover up a truth by misconstruing and misrepresenting it.

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Café Scientifique tonight, in the Twin Cities

I’m going to be driving to the Varsity Theater in Dinkytown this afternoon. It’s time for a Café Scientifique on the subject of “Understanding Evolution” at 6:00 this evening. We have a 3 person panel, with Mark Borello of UMTC talking about the history of evolutionary thought, Scott Lanyon of the Bell Museum describing evolutionary patterns, and me saying a few words about public misconceptions about evolution. It should be fun.

One word on what to expect, though: this is Café Scientifique. It’s not just us three babbling at you; we’re each going to give a 10-15 minute overview, but the main objective is to get the audience talking and asking questions. So show up, but be prepared to contribute!

Next time I’m in New York…

I’m going to have to visit the American Museum of Natural History and see the
new permanent exhibit on human origins. It sounds very good; they’ve done something I try to do in some of my talks on evolution, splitting it between the more easily comprehended, sexy stuff of fossils and reconstructions and the more abstract and more recent material on molecular biology and genetics. There’s an oft-told myth among the creationists that evolution is dying, but it’s precisely that explosion of new information we’re gaining from molecular approaches that has been revitalizing the research for some time now.

The do throw one sop to the culture wars:

One issue cannot be entirely sidestepped in any public presentation of human evolution: that many people in this country doubt and vocally oppose the very concept. In a corner of the hall, several scientists are shown in video interviews professing the compatibility of their evolution research with their religious beliefs.

This is a new permanent exhibit, but I vaguely recall seeing a video presentation like this at a museum somewhere; was it on display at the AMNH before? It’s not a big deal, as what I remember of it was being faintly embarrassed at these scientists professing to be proud of their archaic bone-in-the-nose magic rituals. That part will be skippable—I look forward to seeing the real evidence, that wonderful piece of the universe that is untainted by the delusions of tradition.